Sulfurized polybenzoxazine that can be used for coating metal and for the bonding of same to rubber

ABSTRACT

in which the two oxazine rings are connected together via a central aromatic group, the benzene ring of which bears one, two, three or four groups of formula —Sx—R in which “x” is an integer from 1 to 8 and R represents hydrogen or a hydrocarbon-based group including 1 to 10 carbon atoms and optionally a heteroatom chosen from O, S, N and P. Such a polybenzoxazine can be used as an adhesive layer on metal, in particular for the adhesive bonding of a metallic substrate, in particular made of carbon steel, to rubber.

1. FIELD OF THE INVENTION

The present invention relates to thermosetting resins, which may be used notably in adhesive systems intended in particular for the adhesive bonding of metal to rubber.

The invention relates more particularly to polymers with benzoxazine units or “polybenzoxazines” that may be used in particular as adhesive layers in metal/rubber composites intended for the manufacture of rubber articles such as pneumatic or non-pneumatic tyres, for motor vehicles.

2. PRIOR ART

Metal/rubber composites, in particular for motor vehicle tyres, are well known. They are usually composed of a matrix made of unsaturated rubber, generally diene rubber, which can be crosslinked with sulfur, including metal reinforcing elements (or “reinforcers”) such as yarns, films, tapes or cords made of carbon steel.

As they are subjected to very high stresses during the rolling of the tyres, notably to repeated actions of compression, bending or variations in curvature, these composites must, in a known manner, satisfy a large number of sometimes contradictory technical criteria, such as uniformity, flexibility, flexural strength and compressive strength, tensile strength, wear resistance and corrosion resistance, and must maintain these performance qualities at a very high level for as long as possible.

It is easily understood that the adhesive interphase between rubber and reinforcers plays a predominant role in the endurance of these performance qualities. The conventional process for connecting rubber compositions to carbon steel consists in coating the surface of the steel with brass (copper/zinc alloy), the bonding between the steel and the rubber matrix being provided by sulfurization of the brass during the vulcanization or curing of the rubber. In order to improve the adhesion, use is generally made, in addition, in these rubber compositions, of organic salts or metal complexes, such as cobalt salts, as adhesion-promoting additives.

However, it is known that the adhesion between the carbon steel and the rubber matrix is liable to weaken over time as a result of the gradual development of the sulfides formed, under the effect of the various stresses encountered, notably mechanical and/or thermal stresses, it being possible for the above degradation process to be accelerated in the presence of moisture. Moreover, the use of cobalt salts renders the rubber compositions more sensitive to oxidation and to ageing, and significantly increases the cost thereof, not to mention that it is desirable to eliminate, in the long run, the use of such cobalt salts in rubber compositions due to the recent change in European regulations relating to metal salts of this type.

For all the reasons set out above, manufacturers of metal/rubber composites, in particular motor vehicle tyre manufacturers, are seeking novel adhesive solutions in order to adhesively bond metal reinforcers to rubber compositions, while overcoming, at least in part, the abovementioned drawbacks.

Thus, the recently published patent applications WO 2014/063963, WO 2014/063968, WO 2014/173838 and WO 2014/173839, filed by the Applicant Companies, have described novel polymers bearing urea, urethane or thiourea units, and also their starting monomers, which meet the above objectives. Used notably as adhesion primer on metal in metal/rubber composites, these polymers make it possible very advantageously to adhesively bond the metal to the rubber matrices by subsequently using simple textile adhesives, such as “RFL” (resorcinol/formaldehyde latex) adhesives or other equivalent adhesive compositions, or else directly (that is to say, without employing such adhesives) to these rubber matrices when the latter contain, for example, appropriate functionalized unsaturated elastomers, such as epoxidized elastomers. Thus, the cobalt salts (or other metal salts) can notably be left out of the rubber compositions intended to be connected to brass-coated metal reinforcers.

In continuing their research, the Applicant Companies have found a novel polymer, of thermosetting type, which at room temperature has the same adhesive performance, with respect to metal and rubber, as the abovementioned polymers, but which has, once thermoset (crosslinked), further improved thermal and chemical stability. Moreover, its specific microstructure makes it possible very advantageously to adjust the flexibility of the molecule depending on the particular applications targeted.

3. BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to a polybenzoxazine sulfide whose repeating units include at least one unit corresponding to formula (I) or (II):

in which the two oxazine rings are connected together via a central aromatic group, the benzene ring of which bears one, two, three or four groups of formula —S_(x)—R in which “x” is an integer from 1 to 8 and R represents hydrogen or a hydrocarbon-based group including 1 to 10 carbon atoms and optionally a heteroatom chosen from O, S, N and P.

The invention also relates to the use of such a polybenzoxazine as polymeric coating of a substrate, at least the surface of which is at least partly metallic, in particular for the adhesive bonding of such a substrate to rubber.

The invention also relates to any substrate, at least the surface of which is at least partly metallic, at least said metallic part being coated with the polymer according to the invention.

The invention and the advantages thereof will be easily understood in the light of the detailed description and the implementation examples which follow, and also of FIGS. 1 to 11 which represent or depict:

-   -   the general principle for the synthesis of a benzoxazine         compound starting from three compounds, phenol, formaldehyde and         amine (R=residue of the amine) (FIG. 1a );     -   the (ring-opening) mechanism for opening, by heat input, the         oxazine ring of such a benzoxazine compound (FIG. 1b );     -   a general scheme for the synthesis, starting from a specific         phenol (the symbol “G” will be described in detail later),         paraformaldehyde and a specific aromatic diamine sulfide, of a         benzoxazine of formula (A-0) (Monomer denoted by “M-0”) that can         be used for the synthesis of a polybenzoxazine sulfide in         accordance with the invention (FIG. 2);     -   a possible scheme for the synthesis, starting from a halogenated         phenol (the symbol “Hal” representing a halogen), p-formaldehyde         and the preceding specific aromatic diamine sulfide, of a         particular halogenated benzoxazine of formula (A-1) (Monomer         denoted by M-1) that can be used for the synthesis of a         polybenzoxazine in accordance with the invention (FIG. 3);     -   another possible scheme for the synthesis, starting from another         specific phenol (the symbol “A” will be described in detail         later), p-formaldehyde and the preceding specific aromatic         diamine sulfide, of another benzoxazine of formula (A-2)         (Monomer denoted by M-2) that can be used for the synthesis of a         polybenzoxazine in accordance with the invention (FIG. 4);     -   another possible scheme for the synthesis, starting from a         halogenated phenol, p-formaldehyde and a particular example of         an aromatic diamine sulfide, of another example of a particular         halogenated benzoxazine of formula (A-3) (Monomer denoted by         M-3) that can be used for the synthesis of a polybenzoxazine in         accordance with the invention (FIG. 5);     -   another possible scheme for the synthesis, starting from another         specific phenol, p-formaldehyde and the preceding specific         example of an aromatic diamine sulfide, of another example of a         benzoxazine of formula (A-4) (Monomer denoted by M-4) that can         be used for the synthesis of a polybenzoxazine according to the         invention (FIG. 6);     -   another possible scheme for the synthesis, starting from a         particular example of a phenol (Compound 1: methoxyphenol         bearing ethylenic unsaturation), p-formaldehyde (Compound 2) and         the preceding particular example (Compound 3) of an aromatic         diamine disulfide, of another example of a benzoxazine of         formula (A-5) (Monomer denoted by M-5) that can be used for the         synthesis of a polybenzoxazine sulfide according to the         invention (FIG. 7);     -   a scheme for the general synthesis of an example of a         polybenzoxazine sulfide (Polymer denoted by P-1) according to         the invention, starting from the preceding halogenated         benzoxazine of formula (A-6) (Monomer M-6) and from another         monomer of general formula (B) (Monomer denoted by N) of the         aromatic diol or thiol type; and also this example of a         polybenzoxazine sulfide (Polymer denoted here by P-1′) according         to the invention once its oxazine rings have been opened after         heat treatment of the polymer P-1 (FIG. 8);     -   a scheme for the synthesis of another polybenzoxazine according         to the invention (Polymer P-2′), with its oxazine rings opened,         obtained by homopolymerization of the preceding particular         halogenated benzoxazine of formula (A-5) (Monomer M-5) (FIG. 9);     -   an example of synthesis, starting from brominated phenol         (compound 4), p-formaldehyde (compound 2) and a specific         aromatic diamine disulfide (compound 3), of a particular         brominated benzoxazine of formula (A-7) (Monomer denoted by M-7)         which may be used for the synthesis of polybenzoxazines (Polymer         P-3 and P-3′ of FIG. 11) in accordance with the invention (FIG.         10);     -   finally, an example of synthesis of a polybenzoxazine sulfide         (Polymer by P-3) according to the invention, starting from the         preceding particular halogenated benzoxazine of formula (A-7)         (Monomer M-7) and from another particular monomer of formula         (B-1) (Monomer N-1) of the sulfur-based aromatic diol type         (bearing a thioether function), and also the structure of this         polymer once its oxazine rings have been opened (Polymer denoted         by P-3′) (FIG. 11).

4. DETAILED DESCRIPTION OF THE INVENTION

It will first of all be recalled that benzoxazines are compounds of general formula:

The appended FIG. 1a recalls the general principle of the synthesis of a benzoxazine, in this instance starting (condensation reaction) from one molecule of phenol, from two molecules of formaldehyde and from an amine (R denoting the residue of the amine), with elimination of two molecules of water.

FIG. 1b for its part recalls the mechanism for opening the oxazine ring (ring-opening) of such a compound during a heat input (represented by the symbol Δ).

Numerous benzoxazine compounds or monomers can thus be synthesized using various phenols and amines according to their types of substituents. These substituting groups may subsequently provide polymerizable sites and make possible the synthesis of various benzoxazine polymers (or polybenzoxazines).

Benzoxazines and polybenzoxazines which result therefrom are products which are today well known to a person skilled in the art; to cite but a few publication examples, mention may be made of the papers “Polybenzoxazines—New high performance thermosetting resins: synthesis and properties”; N. N. Ghosh et al., Prog. Polym. Sci., 32 (2007), 1344-1391, or “Recent Advancement on Polybenzoxazine—A Newly Developed High Performance Thermoset”, Y. Yaggi et al., J. Polym. Sci. Part A: Polym. Chem.: Vol. 47 (2009), 5565-5576, and also, for example, of the patents or patent applications U.S. Pat. No. 5,543,516 and WO 2013/148408.

As explained in detail in the above documents, polybenzoxazines have the remarkable ability, at high temperature (for example, typically greater than 150° C., or even greater than 200° C., depending on their particular microstructure), to open their oxazine rings and to thus result in thermosetting polyphenol resin structures.

The specific polybenzoxazine that is the subject of the invention is derived from a benzoxazine (referred to as Monomer M in the present application) of sulfide type which corresponds to the following generic formula (A):

in which formula (A) each benzene nucleus of the two oxazine rings bears at least one (i.e. one or more) radical G; the benzoxazine itself thus bears at least two radicals G.

The (at least) two radicals G, which may be identical or different, are chosen from the group consisting of:

-   -   halogens;     -   groups —OR₁, —SR₁, —NR₂R₃; R₁, R₂ and R₃, which may be identical         or different, representing an alkyl containing 1 to 4 carbon         atoms; and     -   aliphatic hydrocarbon-based groups including 1 to 8 carbon         atoms, or cycloaliphatic hydrocarbon-based groups including 3 to         8 carbon atoms, or aromatic hydrocarbon-based groups including 6         to 12 carbon atoms; these saturated or ethylenically unsaturated         hydrocarbon-based groups also optionally including at least one         heteroatom chosen from O, S, N and P.

In this formula (A) as described previously for the polymer of the invention, the two oxazine rings are connected together via a central aromatic group, the benzene ring or nucleus of which (also referred to as the central benzene ring or nucleus) bears one, two, three or four groups of formula —S_(x)—R in which “x” is an integer from 1 to 8 and R represents hydrogen or a hydrocarbon-based group including 1 to 10 carbon atoms and optionally a heteroatom chosen from O (oxygen), S (sulfur), N (nitrogen) and P (phosphorus).

Similarly, it may be noted in this formula (A) that the two nitrogen atoms of the oxazine rings are, relative to each other, in any position (i.e. ortho, meta or para) on the central benzene nucleus. However, preferably, these two nitrogen atoms are in the meta-position relative to each other; in other words, the starting benzoxazine (Monomer in this case denoted by M-0) from which is derived the polybenzoxazine of the invention then preferentially corresponds to the generic formula (A-0) below:

The appended FIG. 2 gives the scheme for the general synthesis of this benzoxazinone of formula (A-0), with heat input and with elimination of water, starting from a specific phenol bearing at least one (i.e. one or more) radical G, paraformaldehyde and, finally, a specific aromatic diamine sulfide of formula:

in which formula, needless to say, the benzene ring bears one, two, three or four groups of formula —S_(x)—R as defined previously, and may bear other optional substituents (by way of example a methyl or ethyl group).

Preferentially, in this benzoxazine of formula (A) or (A-0), the central benzene nucleus bears two groups of formula —S_(x)—R, these two groups more preferentially being in the meta-position relative to each other on the benzene nucleus. According to another preferential embodiment, “x” is within a range from 1 to 4, more preferentially equal to 1 or 2. R is preferentially an alkyl more preferentially containing 1 to 5 carbon atoms, even more preferentially a methyl or ethyl, in particular a methyl.

The polybenzoxazine of the invention (Polymer P), derived from the benzoxazine of formula (A) described previously, thus has the essential feature of including structural repeating units including at least one unit corresponding to formula (I) (before opening of the oxazine rings) or formula (II) (after ring opening) below:

The term “polymer” should be understood in the present patent application as meaning any homopolymer or copolymer, notably block copolymer, with repeating structural units including at least one unit of formula (I) or (II) above; needless to say, the polymer of the invention may include both units of formula (I) and units of formula (II).

In formula (II) above, a person skilled in the art will immediately understand that the two symbols “*” (which may be identical or different) represent any attachment of the unit to a carbon atom or to a heteroatom (preferably chosen from O, S, N and P), this attachment or bond resulting from the opening of the oxazine rings during a sufficient input of heat (A).

In addition, in the above formulae (I) and (II), as for the monomer of formula (A), one or more hydrogen atoms of at least one or of each benzene nucleus of the two oxazine rings, and also those of the central benzene ring, may optionally also be substituted with various substituents (by way of example a methyl or ethyl group), notably with functional groups (by way of example a vinyl group) capable of promoting the adhesion of the polymer to the metal and/or to the rubber.

Similarly, as for the preceding monomer of formula (A), it may be noted in these formulae (I) and (II) that the two nitrogen atoms of the oxazine rings are, relative to each other, in any position (i.e. ortho, meta or para) on the central benzene nucleus which separates them.

However, preferably, these two nitrogen atoms are in the meta-position relative to each other on the central benzene nucleus; in other words, the polybenzoxazine of the invention then includes at least repeating structural units including (at least) one unit corresponding to formula (I-bis) (before opening of the oxazine rings) or formula (II-bis) (after opening of the rings) below:

In the preceding formula (A) or (A-0), preferably, each benzene nucleus of the two oxazine rings bears only one radical G or at most two, more preferentially only one radical G.

This radical (radical G) is even more preferentially located in the para position relative to the oxygen of the oxazine ring. In such a case, it will be understood that the polybenzoxazine of the invention thus has the essential feature of including at least repeating structural units including (at least) one unit corresponding to formula (I-a) (before opening of the oxazine rings) or formula (II-a) (after ring opening) below:

Even more preferentially, “x” is equal to 1 and R represents a methyl.

Thus, as examples of aromatic diamine sulfides that are suitable for the synthesis of a benzoxazine of formula (A) or (A-0) in which, according to a particularly preferential embodiment, “x” is equal to 1 and R represents a methyl, mention will be made in particular of the compounds 3,5-bis(methylthio)-2,4-toluenediamine, 3,5-bis(methylthio)-2,6-toluenediamine and mixtures thereof, corresponding, respectively, to formulae (a) and (b) below:

In other words, according to a particularly preferential embodiment, if the benzoxazine of formula (A-0) is derived from at least one of the above two isomers or from mixtures thereof, then the polybenzoxazine of the invention includes repeating units including at least one unit corresponding to formula (I-a-1) or (I-b-1) (before opening of the oxazine rings), (II-a-1) or (II-b-1) (after ring opening) below:

According to a preferential embodiment, the (at least two) radicals G, which may be identical or different, represent a halogen such as bromine, chlorine, fluorine or iodine.

The appended FIG. 3 is a scheme of the general synthesis, with heat supply and with elimination of water, starting from a halogenated phenol bearing at least one (i.e. one or more) halogen (represented by the symbol “Hal”), p-formaldehyde and the specific aromatic diamine sulfide of the preceding FIG. 2, of a particular halogenated benzoxazine of formula (A-1) (Monomer denoted by M-1) which may be used for the synthesis of a polybenzoxazine in accordance with the invention. This halogen (Hal) is more preferentially bromine or chlorine, even more preferentially bromine; the latter even more preferentially being in the para position relative to the oxygen of each oxazine ring.

According to another preferential embodiment, the (at least two) radicals G, which may be identical or different, represent a group chosen from —OR₁, —SR₁, —NR₂R₃; R₁, R₂ and R₃, which may be identical or different, representing an alkyl containing 1 to 4 carbon atoms.

According to another preferential embodiment, the (at least two) radicals G, which may be identical or different, represent an aliphatic hydrocarbon-based group (represented by the symbol “A”) including 1 to 8 carbon atoms, or a cycloaliphatic hydrocarbon-based group including 3 to 8 carbon atoms, or an aromatic hydrocarbon-based group including 6 to 12 carbon atoms, this saturated or ethylenically unsaturated hydrocarbon-based group “A” being able optionally to include a (at least one) heteroatom chosen from O, S, N and P.

The appended FIG. 4 is a scheme of the general synthesis, with heat supply and with elimination of water, starting from a halogenated phenol bearing at least one (i.e. one or more) such group “A”, paraformaldehyde and the specific aromatic diamine sulfide of the preceding FIGS. 2 and 3, of a particular benzoxazine of formula (A-2) (Monomer denoted by M-2) which may be used for the synthesis of a polybenzoxazine in accordance with the invention.

FIG. 5 is another possible scheme for the synthesis, starting from a halogenated phenol, paraformaldehyde and a specific example of an aromatic diamine disulfide, namely 3,5-bis(methylthio)-2,6-toluenediamine of the preceding formula (b), of another example of a particular halogenated benzoxazine of formula (A-3) (Monomer denoted by M-3) that can be used for the synthesis of a polybenzoxazine in accordance with the invention.

FIG. 6 is another possible scheme for the synthesis, starting from another phenol (the symbol “A” has been described previously), paraformaldehyde and 3,5-bis(methylthio)-2,6-toluenediamine of the preceding formula (b), of another example of a benzoxazine of formula (A-4) (Monomer denoted by M-4) that can be used for the synthesis of a polybenzoxazine according to the invention.

According to a preferential embodiment, the (at least two) groups “A”, which may be identical or different, represent an saturated or ethylenically unsaturated aliphatic hydrocarbon-based group, including 1 to 6 and in particular 1 to 4 carbon atoms, which may optionally include at least one (i.e. one or more) heteroatom chosen from O, S, N and P.

Thus, according to another particular and preferential embodiment, the polymer of the invention is derived from a benzoxazine disulfide which corresponds at least partly to one of the two formulae (A-5) and (A-5bis) (Monomers denoted, respectively, by M-5 and M-5bis) below:

FIG. 7 is a particular case of FIG. 6 which describes another scheme for the synthesis, starting this time from a particular example of a phenol (Compound 1) corresponding to such a preferential definition (in this case, phenol bearing an ethylenic unsaturation and a methoxyl group), paraformaldehyde (Compound 2) and the particular example of the preceding aromatic diamine disulfide (Compound 3), of another example of a benzoxazine of formula (A-5) (Monomer denoted by M-5) which may be used for the synthesis of a polybenzoxazine sulfide according to the invention.

A person skilled in the art is well aware of how to widely adapt specific formula (A) or (A-0) of the benzoxazine serving as starting monomer for the synthesis of the polybenzoxazine according to the invention, by notably varying the formulae of the phenol (bearing the radical(s) G) and of the diamine sulfide (bearing the group(s) of formula —S_(x)R).

As examples of preferential aromatic diamine sulfides, mention has already notably been made of the compounds 3,5-bis(methylthio)-2,4-toluenediamine, 3,5-bis(methylthio)-2,6-toluenediamine, and mixtures thereof.

As examples of phenol compounds (in this case, for example, methoxyphenols) bearing groups “A” of the saturated or ethylenically unsaturated aliphatic hydrocarbon-based type, including 1 to 6 and in particular 1 to 4 carbon atoms, which may optionally include at least one (i.e. one or more) heteroatom chosen from O, S, N and P, examples that may be mentioned include the following compounds:

According to a preferential embodiment, the polybenzoxazine polymer of the invention may be obtained by polycondensation of a benzoxazine of formula (A) or (A-0) as described in detail previously, as first monomer, and, as second monomer, an aromatic diol or thiol compound.

This aromatic diol or thiol compound more preferentially corresponds to formula (B):

HX₁—Ar₁—Z—Ar₂—X₂H  (B)

in which:

-   -   X₁ and X₂, which may be identical or different, represent O or         S;     -   Ar₁ and Ar₂, which may be identical or different, represent an         aromatic group, preferably phenylene;     -   Z represents O or (S)_(n), the symbol “n” representing an         integer greater than or equal to 1.

Thus, according to one particularly preferred embodiment, the polybenzoxazine of the invention is characterized by repeat units including at least one unit corresponding to the particular formulae (I-1) (before opening of the oxazine rings) or (II-1) (after ring opening):

In this case also, it is clearly noted that, in the above formulae, the two nitrogen atoms of the oxazine rings are, relative to each other, in any position (i.e. ortho, meta or para) on the central benzene nucleus which separates them.

However, even more preferentially, in the above formulae (I-1) and (II-1) above, these two nitrogen atoms are in the meta-position relative to each other on the central benzene nucleus which separates them. In other words, the polybenzoxazine of the invention then includes repeating structural units including (at least) one unit corresponding to formula (I-1bis) (before opening of the oxazine rings) or formula (II-1bis) (after ring opening) below:

In the above formulae (I-1), (II-1), (I-1bis) and (II-1bis), one or more hydrogen atoms of at least one or of each aromatic nucleus Ar₁ and Ar₂ could be substituted with various substituents, which may be identical or different, for example functional groups capable of promoting the adhesion of the polymer to the metal and/or to the rubber.

FIG. 8 is a scheme for the general synthesis of a polybenzoxazine sulfide (Polymer denoted by P-1) according to the invention, of formula (I-1bis) above, starting from the preceding halogenated benzoxazine of formula (A-6) (Monomer M-6) and from another monomer of general formula (B) (Monomer denoted by “N”) of the aromatic diol or thiol type; and also this example of a polybenzoxazine sulfide (Polymer denoted here by P-1′ of formula II-1bis) according to the invention once its oxazine rings have been opened after heat treatment of the polymer P-1.

In the general formulae (I-1), (II-1), (I-1bis) or (II-1bis) above, preferentially at least one of the following features is satisfied:

-   -   Ar₁ and Ar₂ each represent an unsubstituted phenylene group;     -   X₁ and X₂ each represent either a sulfur atom, or an oxygen         atom;     -   Z represents O or S (i.e. “n” equal to 1), more preferentially         S.

More preferentially, it is all of the preferential features above which are simultaneously satisfied.

As preferential examples, the compound of the preceding formula (B) corresponds to at least one of the particular formulae (B-1), (B-2) or (B-3) below:

According to another particular and preferential embodiment, the polybenzoxazine polymer of the invention may be obtained by homopolymerization of a benzoxazine of formula (A) or (A-0) as described above.

Thus, FIG. 9 illustrates a scheme for the synthesis of another polybenzoxazine according to the invention (Polymer P-2′ of formula II-2), with its oxazine rings opened, this time obtained by simple homopolymerization of the particular halogenated benzoxazine of the preceding formula (A-5) (Monomer M-5).

According to another particular and preferential embodiment, the polymer of the invention is derived from a brominated benzoxazine polysulfide which corresponds at least partly to one of the two formulae (A-7) and (A-7bis) (Monomers denoted, respectively, by M-7 and M-7bis) below:

FIG. 10 precisely gives an example of synthesis, starting from the brominated phenol (compound 4), p-formaldehyde (compound 2) and 3,5-bis(methylthio)-2,6-toluenediamine (compound 3), of this brominated benzoxazine polysulfide of formula (A-7) (Monomer denoted by M-7) which may be used for the synthesis of polybenzoxazines (Polymer P-3 and P-3′ of FIG. 11) in accordance with the invention.

In these examples of FIG. 10, as for the preceding FIGS. 7 to 9, it is noted in particular, according to a particularly preferential embodiment of the invention already indicated, that each benzene nucleus of the two oxazine rings of the benzoxazine of formula (A) bears only one halogen (Hal), more preferentially bromine, located in the para position relative to the oxygen of the oxazine ring.

Finally, FIG. 11 describes the synthesis of a polybenzoxazine sulfide (Polymer P-3) according to the invention, starting from the particular halogenated benzoxazine of formula (A-7) (Monomer M-7) above and from another particular monomer of formula (B-1) (Monomer N-1) of the sulfur-based aromatic diol type (bearing a thioether function), and also the structure of this polymer once its oxazine rings have been opened (Polymer denoted by P-3′).

The syntheses of FIGS. 10 and 11 will be described in greater detail in the implementation examples that follow.

Typically, the polybenzoxazine of the invention may include from ten to several hundred, preferably from 50 to 300, structural units bearing units of formula (I) and/or (II), in particular structural units as represented as examples in FIGS. 8, 9 and 11.

The polybenzoxazine of the invention may advantageously be used, as adhesion primer or as sole adhesive layer, for coating a metal substrate, at the very least a substrate of which at least the surface is at least partly metallic, and notably making this substrate adhere to rubber.

The invention also relates to such a substrate, notably made of steel such as a carbon steel. The steel may be bright (i.e. uncoated) or may be at least partly coated with at least one layer (thus an intermediate layer positioned between the steel and the polybenzoxazine layer) of a second metal known as the surface metal, chosen from the group consisting of aluminium, copper, zinc and alloys of at least one of these metals with at least one other metal (belonging or not belonging to this group). This surface metal is in particular brass.

In order to adhere the rubber to the polybenzoxazine layer, use may be made of any known adhesive system, for example a conventional textile adhesive of “RFL” type comprising at least one diene elastomer such as natural rubber, or any equivalent adhesive known for imparting satisfactory adhesion between rubber and conventional polymers such as polyester or polyamide, for instance the adhesive compositions described in patent applications WO 2013/017421, WO 2013/017422, WO 2013/017423, WO 2015/007641, and WO 2015/007642.

Before the above adhesive coating process, it may be advantageous to activate the surface of the polymer of the invention, for example physically and/or chemically, to improve the adhesive uptake thereof and/or the final adhesion thereof to the rubber. A physical treatment may consist, for example, of a treatment by radiation such as an electron beam, or by plasma; a chemical treatment may consist, for example, of prior passage through a bath of epoxy resin and/or isocyanate compound.

A person skilled in the art will readily understand that the connection between the metal substrate provided with its polybenzoxazine layer and the rubber layer with which it is in contact will be definitively provided during the final curing (crosslinking) of the rubber article in question.

5. IMPLEMENTATION EXAMPLES OF THE INVENTION

In the present patent application, unless expressly indicated otherwise, all the percentages (%) shown are mass percentages.

The following tests firstly describe the synthesis of two examples of benzoxazine compounds (Monomers M-5 and M-7), then that of a preferential polybenzoxazine (Polymer P-3) according to the invention, starting from the Monomer M-7. Lastly, adhesion tests are performed to illustrate the excellent adhesive performance of the polybenzoxazines of invention.

5.1. Synthesis of a Benzoxazine Sulfide (Monomer M-5)

For this synthesis, a 100-ml three-necked round-bottomed flask, equipped with a thermometer, a nitrogen inlet, a magnetic stirrer and a condenser, is provided.

The synthesis is performed according to the procedure depicted in FIG. 7, as explained in detail below, starting with three compounds: a specific ethylenically unsaturated phenol bearing a methoxyl group (compound 1; eugenol; Aldrich product E51791), paraformaldehyde (compound 2; Aldrich product 158127) and an aromatic diamine disulfide (compound 3; 3,5-bis(methylthio)-2,6-toluenediamine), in the presence of two solvents (anhydrous toluene and anhydrous ethanol).

Compound 3 was isolated, by chromatography on silica gel, from the product Ethacure 300 (supplier: Albemarle, Belgium), available in the form of a relatively viscous liquid of brownish colour; it is composed to approximately 96% of a mixture of 3,5-bis(methylthio)-2,4-toluenediamine and 3,5-bis(methylthio)-2,6-toluenediamine isomers (weight ratio of approximately 4/1 according to chromatographic analysis).

Compound 1 (2 eq., 4.93 g, i.e. 30 mmol) and then ethanol (51 ml) are poured into the round-bottomed flask. The presence of ethanol is important in this instance, preventing the formation of an unstable triazine-type intermediate product. Compound 3 (1 eq., 3.215 g, i.e. 15 mmol), compound 2 (4 eq., 1.80 g, i.e. 60 mmol) and finally the toluene (102 ml) are subsequently introduced with stirring. The reaction medium is heated (approximately 75° C.) at reflux for 4 h and, after distilling off the ethanol at about 100° C. over 16 hours, the solvents and volatile residues are then finally distilled off at 40° C. (under a vacuum of 20 mbar) for evaporation. The final product is then washed (100 ml of methanol) and dried.

This powder is placed in methanol (50 ml per 4 g of powder) and the mixture is heated at reflux (65° C.) for 30 min. The solution is then left to cool to room temperature (approximately 20° C.) for crystallization of the monomer. The solid product obtained is isolated by filtration (Büchner filter). After drying in a vacuum oven at 50° C. overnight, a powder is thus obtained, the ¹H NMR spectrum (500 MHz) (solvent: d8-THF) of which confirmed the chemical structure of the Monomer M-5 thus synthesized, with the following results:

2.07 (s, 3H), 2.38 (s, 6H), 3.25 (t, 4H), 3.71 (s, 6H), 3.94-4.01 (t, 2H), 4.58-4.64 (dd, 2H), 4.81-4.86 (dd, 2H), 4.96-5.05 (m, 6H), 5.85-5.97 (m, 2H), 6.37-6.40 (d, 2H), 6.55 (s, 2H), 6.72 (s, 1H).

5.2. Synthesis of a Halogenated Benzoxazine Sulfide (Monomer M-7)

For this synthesis, a 100-ml three-necked round-bottomed flask, equipped with a thermometer, a nitrogen inlet, a magnetic stirrer and a condenser, is provided.

The synthesis is performed according to the procedure depicted in FIG. 10, as explained in detail below, starting with three compounds: a halogenated phenol (compound 4; 4-bromophenol; Aldrich product B75808), p-formaldehyde (compound 2; Aldrich product 158127) and an aromatic diamine disulfide (compound 3; 3,5-bis(methylthio)-2,6-toluenediamine), in the presence of two solvents (anhydrous toluene and anhydrous ethanol).

Compound 3 was isolated, by chromatography on silica gel, from the product Ethacure 300 (supplier: Albemarle, Belgium), available in the form of a relatively viscous liquid of brownish colour; it is composed to approximately 96% of a mixture of 3,5-bis(methylthio)-2,4-toluenediamine and 3,5-bis(methylthio)-2,6-toluenediamine isomers (weight ratio of approximately 4/1 according to chromatographic analysis).

Compound 4 (2 eq., 2.6 g, i.e. 15 mmol) and then ethanol (23 ml) are poured into the round-bottomed flask. The presence of ethanol is important in this instance, preventing the formation of an unstable triazine-type intermediate product. Compound 3 (1 eq., 1.6 g, i.e. 7.5 mmol), compound 2 (4 eq., 0.90 g, i.e. 30 mmol) and finally the toluene (46 ml) are subsequently introduced with stirring. The reaction medium is heated (approximately 75° C.) at reflux for 16 h and then the solvents and volatile residues are distilled off at 40° C. under vacuum (20 mbar) for evaporation.

The final product is then placed in methanol (50 ml per 4.5 g of product) and the mixture is heated at reflux (65° C.) for 30 min. The solution is then left to cool to room temperature (approximately 20° C.) for crystallization of the monomer. The solid product obtained is isolated by filtration (Büchner filter). A yellow powder is thus obtained, after drying in a vacuum oven at 50° C. overnight (reaction yield equal to approximately 82%).

The ¹H NMR spectra (500 MHz) of the Monomer M-7 thus synthesized, dissolved in a deuterated solvent, confirmed its chemical structure, with the following results:

-   -   in d8-THF:

2.06 (s, 3H), 2.39 (s, 6H), 4.03-4.14 (t, 2H), 4.59-4.63 (d, 2H), 4.87-4.91 (dd, 2H), 5.01-5.05 (dd, 2H), 6.71-6.74 (d, 2H), 6.81 (s, 1H), 7.15-7.21 (m, 4H);

-   -   in CD₂Cl₂:

2.06 (s, 3H), 2.39 (s, 6H), 4.03-4.14 (t, 2H), 4.53-4.58 (dd, 2H), 4.92-4.95 (dd, 2H), 5.00-5.04 (dd, 2H), 6.68 (s, 1H), 6.74-6.77 (d, 2H), 7.14-7.15 (d, 2H), 7.21-7.24 (dd, 2H).

5.3. Synthesis of a Polybenzoxazine Polysulfide According to the Invention (Polymer P-3)

This synthesis is performed according to the procedure depicted in the FIG. 11, as described in detail below, starting with two monomers: the benzoxazine obtained in the preceding step (Monomer M-7) and the sulfur-bearing aromatic diol of formula (B-1) (4,4′-thiodiphenol; Monomer N-1); this being in the presence of sodium carbonate (Na₂CO₃; Sigma Aldrich product 13418), and the (anhydrous) solvents DMA (N,N-dimethylacetamide; Sigma Aldrich product 38839) and toluene (Acros Organics product No. 364411000). The two monomers (M-7 and N-1) are dried beforehand under vacuum (10 mbar) at 60° C. overnight, and likewise for the sodium carbonate but at a temperature of 150° C.

The synthesis is performed in a 100-ml four-necked round-bottomed flask, equipped with a nitrogen inlet, a thermometer, a magnetic stirrer and a Dean-Stark separator surmounted by a condenser and by a distillation bridge (provided with a heating mantle). The apparatus is dried under vacuum using a hot air gun until the thermometer reaches a temperature of at least 100° C. in the reaction flask. The system is left to cool to room temperature (20° C.) and the apparatus is then placed under a stream of nitrogen throughout the synthesis.

First of all, the Monomer M-7 (1 eq., 1.5 g, i.e. 2.79 mmol) of formula (A-7) and then the Monomer N-1 of formula (B-1) (1 eq., 0.61 g, i.e. 2.79 mmol) are then introduced into the round-bottomed flask. This is followed by addition of 20 ml of DMA (solvent of both monomers) and then, as base, of Na₂CO₃ (3 eq., 0.89 g, i.e. 8.36 mol) suspended in 4 ml of toluene. The system is purged under N₂ for 5 min and the reaction medium is then heated to 105° C. Once this temperature is reached (heating mantle temperature of approximately 115° C.), the distillation bridge of the Dean-Stark apparatus is heated to 110° C. (with the heating mantle) in order to facilitate the azeotropic distillation (water/toluene distillation) performed for approximately 90 min. The temperature of the reaction medium is then gradually increased, in stages of 10° C. every 30 min, until 130° C. is reached. The reaction medium is left at this temperature for 17 h and is then left to cool to room temperature (20° C.). The reaction mixture is subsequently distilled at 90° C. (vacuum 3 mbar) to remove the solvents and volatile residues, and the solid precipitate thus obtained is then washed with 250 ml of distilled water; during this washing, to extract the carbonate, acid (1% aqueous HCl) is added dropwise until neutral pH is reached. The precipitate is once again washed with 100 ml of distilled water and dried under vacuum at 80° C. overnight (approximately 12 h).

The Polymer P-3 of FIG. 11 was thus obtained, as attested to by the ¹H NMR analysis (500 MHz) in the solvent d8-THF, which gave the following results:

1.92 (s, 3H), 2.26 (s, 6H), 3.74-3.81 (m, 4H), 4.01-4.03 (t, 2H), 4.75-5.01 (m, 2H), 6-15-6.75 (m, 4H), 6.90-7.45 (br, 11H).

This Polymer P-3, in the form of a pale yellow powder, was also analysed by DSC (Differential Scanning calorimetry) between −80° C. and +350° C. with a ramp of 10° C./min (Mettler Toledo DSC “822-2” machine; nitrogen atmosphere). The analysis showed, in the first pass (between −80° C. and +350° C.), an apparent glass transition (Tg) at 163° C. followed by exothermicity (corresponding to the opening of the oxazine rings and to the crosslinking of the polymer) above 200° C., with two maxima at approximately 270° C. and 299° C. During the second and third DSC passes, performed between −80° C. and +350° C., no apparent glass transition was visible.

5.4. Test of Adhesion in a Metal/Rubber Composite

A portion (325 mg) of the Polymer P-3 prepared above was dissolved in 8 ml of DMPU (1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone; Sigma Aldrich product 41661) with 10% by weight of “DY 9577 ES” accelerator (Huntsman product), this being in order to form a solution, a fraction (0.6 ml) of which was subsequently deposited uniformly on a brass tape (film) having dimensions of 10 cm×2.5 cm and a thickness of 0.5 mm; the assembly was placed in an oven at 175° C. (air ventilation) for 5 min and then for an additional 5 min at 230° C. under vacuum in order, firstly, to remove any trace of solvent and, secondly, to at least partially (that is to say, completely or partially) open the oxazine rings of the polymer, this last step being accompanied by a pronounced change in colour of the polymer, which changes to dark orange.

After cooling to room temperature, the tape provided at the surface with its thin (thickness 5 to 10 μm) layer of polybenzoxazine thus formed was subsequently subjected to a conventional two-stage adhesive coating operation (two baths adhesive coating), first of all by immersion in a first aqueous bath (approximately 94% water) based on epoxy resin (polyglycerol polyglycidyl ether, approximately 1%) and on isocyanate compound (caprolactam-blocked isocyanate compound, approximately 5%), this first adhesive coating step being followed by drying (2 min at 100° C.) and then a heat treatment (5 min at 200° C.).

The tape thus treated was then immersed in a second aqueous bath of RFL adhesive (approximately 81% by weight of water) based on resorcinol (approximately 2%), on formaldehyde (approximately 1%) and on a rubber latex (approximately 16% of NR, SBR and VP/SBR rubbers); finally, it was dried in an oven at 130° C. for 2 min and then heat treated at 200° C. for 5 min.

The brass tape thus coated with the polybenzoxazine film and then coated with adhesive was subsequently placed between two layers of conventional rubber composition for a belt reinforcement of a passenger vehicle tyre, this composition being based on natural rubber, on carbon black and silica as filler and on a vulcanization system (sulfur and sulfenamide accelerator); this composition was free of cobalt salt. The metal/rubber composite test specimen thus prepared was then placed under a press and the whole was cured (vulcanized) at 150° C. for 30 min under a pressure of 20 bar.

After vulcanization of the rubber, excellent adhesive bonding between the rubber matrix and the metal tape of the invention was obtained, despite the absence of cobalt salt in the rubber matrix; this is because, during peel tests (at 20° C.), it was found that the failure occurred systematically in the rubber matrix itself and not at the interphase between metal and rubber. Other adhesive bonding tests were performed on a bright (uncoated) steel tape; they also revealed excellent adhesion to the rubber (systematic failure in the rubber matrix).

In conclusion, the polybenzoxazine according to the invention offers the metal substrates the major advantage of being able subsequently to be adhesively bonded to rubber matrices using simple textile adhesives, such as RFL adhesives, or else directly (that is to say, without employing such adhesives) to these rubber matrices, for example when the latter contain appropriate functionalized unsaturated elastomers, such as epoxidized elastomers. Thus, use may be made of metal substrates optionally coated with adhesive metal layers such as brass, and also surrounding rubber matrices free of metal salts, in particular of cobalt salts.

Moreover, this constituting a significant advantage compared to the other known polymers described in the introduction to the present document, the polybenzoxazines of the invention have the noteworthy ability, at high temperature, to open their oxazine rings and to thus give a thermosetting polyphenolic resin structure. This gives them better heat stability. Finally, their specific microstructure makes it possible, very advantageously, to adjust the flexibility of the molecule according to the particular applications targeted. 

1.-19. (canceled)
 20. A polybenzoxazine sulfide, repeating units of which include at least one unit corresponding to formula (I) or (II):

in which the two oxazine rings are connected together via a central aromatic group, the benzene ring of which bears one, two, three or four groups of formula —S_(x)—R in which x is an integer from 1 to 8 and R represents hydrogen or a hydrocarbon-based group including 1 to 10 carbon atoms and optionally a heteroatom chosen from O, S, N and P.
 21. The polybenzoxazine sulfide according to claim 20, wherein the central benzene ring bears two groups of formula —S_(x)—R.
 22. The polybenzoxazine sulfide according to claim 21, wherein the two groups of formula —S_(x)—R are in the meta-position relative to each other on the central benzene ring.
 23. The polybenzoxazine sulfide according to claim 20, wherein x is in a range from 1 to
 4. 24. The polybenzoxazine sulfide according to claim 20, wherein R is an alkyl containing from 1 to 5 carbon atoms.
 25. The polybenzoxazine sulfide according to claim 24, wherein R represents a methyl or an ethyl.
 26. The polybenzoxazine sulfide according to claim 23, wherein x is equal to 1 and R represents a methyl.
 27. The polybenzoxazine sulfide according to claim 20, the repeating units of which comprise at least one unit corresponding to formulae (I-bis) or (II-bis):


28. The polybenzoxazine sulfide according to claim 27, the repeating units of which comprise at least one unit corresponding to formulae (I-a) or (II-a):


29. The polybenzoxazine sulfide according to claim 28, the repeating units of which comprise at least one unit corresponding to formulae (I-a-1), (I-b-1), (II-a-1) or (II-b-1):


30. The polybenzoxazine sulfide according to claim 20, the repeating units of which correspond to at least one of the formulae (I-1) or (II-1) below:

in which: X₁ and X₂, which may be identical or different, represent O or S; Ar₁ and Ar₂, which may be identical or different, represent an aromatic group; and Z represents O or (S)_(n), n representing an integer greater than or equal to
 1. 31. The polybenzoxazine sulfide according to claim 30, the repeating units of which correspond to at least one of the formulae (I-1bis) or (II-1bis) below:


32. A method for polymeric coating of a substrate, wherein at least a surface of the substrate is at least partly metallic, comprising the step of: coating the substrate with a polybenzoxazine sulfide according to claim 20 to form a coated substrate.
 33. The method according to claim 32, wherein the coated substrate is bonded to a rubber.
 34. A substrate having at least a surface which is at least partly metallic, the at least partly metallic surface being coated with a polybenzoxazine sulfide according to claim
 20. 35. The substrate according to claim 34, wherein the substrate is made of steel.
 36. The substrate according to claim 35, wherein the steel is a bright steel.
 37. The substrate according to claim 35, wherein the steel is at least partially coated with at least one layer of a second surface metal selected from the group consisting of aluminum, copper, zinc and alloys thereof.
 38. The substrate according to claim 37, wherein the second surface metal is brass.
 39. The polybenzoxazine sulfide according to claim 25, wherein x is equal to 1 and R represents a methyl. 